Add link to Lecture 13 video

README.md

@@ -21,7 +21,7 @@
 | 10 | Мрежово програмиране (част I) | [слайдове](https://fmi.github.io/java-course/10-network/lecture/slides.html#22) | [![Video](web/images/mjt-on-youtube.png)](https://www.youtube.com/watch?v=IA81iE5Rmzk&t=1h21m36s) | 13.12 | [задача](https://github.com/fmi/java-course/tree/master/10-network/lab) | [![Video](web/images/mjt-on-youtube.png)](https://youtu.be/K5yuHoj3Y5M) | 16.12 |
 | 11 | Мрежово програмиране (част II) | [слайдове](https://fmi.github.io/java-course/11-network-ii/lecture/slides.html) | [![Video](web/images/mjt-on-youtube.png)](https://youtu.be/l0PFmfJU6GI) | 20.12 |  |  |  |
 | 12 | HTTP, REST и JSON | [слайдове](https://fmi.github.io/java-course/12-http-rest/lecture/slides.html) | [![Video](web/images/mjt-on-youtube.png)](https://youtu.be/eZ8fTXGB7s8) | 03.01 | [задача](https://github.com/fmi/java-course/tree/master/12-http-rest/lab) | [![Video](web/images/mjt-on-youtube.png)](https://youtu.be/OJZr7uHW9YM) | 06.01 |
-| 13 | Design Patterns | [слайдове](https://fmi.github.io/java-course/13-design-patterns/lecture/slides.html) |  | 10.01 |  |  |  |
+| 13 | Design Patterns | [слайдове](https://fmi.github.io/java-course/13-design-patterns/lecture/slides.html) | [![Video](web/images/mjt-on-youtube.png)](https://youtu.be/ctM52Dfnnfw) | 10.01 |  |  |  |
 
 ### Материали от предходни издания